blimey, no wonder it took along time to answer
only joking that must have taken sum working out
Cant remember all of mine at the mo. other than the one I already mentioned, some sort of sundial (time) and something in maths found on tinternet were the rings slowly nest together, it was called nesting something or other.
must make note in future if we are going to list them. I have not tried anything since the clue, its a real taxing one